1. Field of the Invention
The present invention relates to a method of restricting the use of software in order to protect it from illicit use.
2. Description of the Background Art
Software available on the market for use in a computer is generally allowed to be used only by a person having purchased it. However, because such software is versatile, it is likely that the software is illicitly copied and used on another computer not authorized. Computers are provided with a keyboard or similar manual input unit on which the user of the computer can input various kinds of information.
On the other hand, there is software preinstalled in a refrigerator, microwave oven or similar household electrical appliance provided with or without some kind of manual input unit. Let this kind of software be referred to as preinstalled software hereinafter. In a broader sense, software already installed in computers prior to marketing may also be referred to as preinstalled software.
In any case, preinstalled software is usually expected to be used only by hardware in which it is preinstalled, i.e. allowed to be used on hardware produced by a particular manufacturer, but inhibited from being used on hardware produced by other manufacturers not authorized. However, if software preinstalled in hardware produced by a particular manufacturer is versatile, then it is likely that the preinstalled software is illicitly copied and used on other hardware not authorized, i.e. another kind of hardware. When such illicit use of the preinstalled software is revealed, that particular manufacturer is able to take legal means for claiming damages. Usually, however, it is difficult to expose this kind of illicit use.
In light of the above, Japanese patent laid-open publication Nos. 219761/1995, 2002-258963 and 2004-171500, for example, disclose particular methods of protecting software from illicit use. Publication No. 219761/1995, for example, teaches a method that urges a person to input a keyword on a keyboard or manual input unit and then allows, if the keyword is correct, the person to operate software. This kind of method has, however, some problems left unsolved, as will be described hereinafter.
The software protecting methods taught in the above-indicated prior art documents are not practicable because of resorting to a manual input unit and a password to be input on the input unit, and therefore not applicable to software preinstalled in specific sorts of hardware provided with a hardware-specific type of manual input unit or without being provided with any manual input unit, such as popular household electrical appliances.
Further, the conventional software protecting methods take measures of, when the illicit use of the software is determined, limiting the functions available with that software or practically inhibiting the whole software from being operative. This, however, allows a user to learn the software protection rendered operative, and therefore become aware of a protection program sequence embedded in just before the program step of that software restricted in operation or made inoperative. Stated in another way, a protection program sequence can be relatively easily decoded if the execution history thereof is traced. Consequently, the user may succeed in invalidating the protection program sequence although spending time. The protection program sequence, therefore, fails to fully obviate illicit use of software.